Steering system including tandem hydraulic cylinders with self-synchronization

Abstract

The invention is especially suitable when front and rear wheels are hydraulically steered, each set by its own hydraulic cylinder, the two cylinders being connected in hydraulic tandem so that the same angularity of steering will be imparted to both sets of wheels. The self-synchronizing of the present invention overcomes a serious prior fault that occasionally a nonsynchronous relationship would develop. The present invention opens a synchronizing valve on the occasion of each extreme swing of the wheels. A check valve then ensures a synchronized return swing.

I claim: 
     
       1. A steering system for use with front and rear steerable wheels, including a pair of cylinder-piston combinations, one for front-wheel steering and one for rear-wheel steering, having cylinders, each with a piston rod extending through at least one end, at times connected through a tandem line connecting a rod end of each to the other, steering valve means for reversably connecting the opposite ends at will to pressure and return lines respectively to operate either combination as a primary piston and cylinder, with development of a primary pressure therein, and the other as a secondary piston and cylinder operated by discharge from the primary cylinder, having the improvement which comprises: a synchronizing valve assembly including a synchronizing valve having means biasing it to be normally closed; solely-mechanical means including one of said piston rods, extending from one of said pistons and engaging the syhchronizing valve to actuate said valve by force derived from said one piston, when primary pressure moves said one piston to the extreme end of its movement, to supply pressure oil at the primary pressure through a check valve to the tandem line, thereby ensuring full movement of the other or secondary piston, said synchronizing valve being held open by said mechanical action until retraction of said one piston by pressure in the tandem line allows said synchronizing valve to close, said check valve preventing loss of pressure in the tandem line by outflow through the synchronizing valve while held open.   
     
     
       2. A steering system for use with front and rear steerable wheels including a pair of cylinder-piston combinations, one for front-wheel steering and one for rear-wheel steering, having cylinders, each with a piston rod extending through at least one end, at times connected through a tandem line connecting a rod end of each to the other, steering valve means for reversably connecting the opposite ends at will to pressure and return lines respectively to operate either combination as a primary piston and cylinder, with development of a primary pressure therein, and the other as a secondary piston and cylinder operated by discharge from the primary cylinder, having the improvement which comprises: a synchronizing valve assembly including a synchronizing valve having means biasing it to be normally closed; solely-mechanical means including one of said piston rods, extending from one of said pistons and engaging the synchronizing valve to actuate said valve by force derived from said one piston, when primary pressure moves said one piston to the extreme end of its movement, to supply pressure oil at the primary pressure through a check valve to the tandem line, thereby ensuring full movement of the other or secondary piston, said synchronizing valve being held open by said mechanical action until retraction of said one piston by pressure in the tandem line allows said synchronizing valve to close, said check valve preventing loss of pressure in the tandem line by outflow through the synchronizing valve while held open; and   a pressure-relief valve responsive to static pressure developed in the tandem line as maximum available primary pressure is closely approached when the secondary piston reaches the full movement before the primary piston does, for allowing escape of oil from the tandem line when an excess of tandem oil would otherwise prevent full-stroke operation of the primary piston.